Causality
by NeverMineToHold
Summary: Action and reaction. For Tron, it begins with CLUs creation, develops further with Kevin Flynn changing and ends with him needing to make a choice: to fight for the Grid or for its User.


Title: „Causality"

Status: OneShot; Complete

Fandom: Tron: Legacy

Characters: Tron, CLU, Kevin Flynn

Word Count: 3657

Disclaimer: The big mouse owns half the world, both Tron movies included.

Rating: T

Genre: itsy bitsy bit dark, H/C, angst, friendship

Beta: The great ScribeOfRED! Thank you so very much for your help; your input really brushed this up a lot!

Summary: Action and reaction. For Tron, it begins with CLUs creation, develops further with Kevin Flynn changing and ends with him needing to make a choice: to fight for the Grid or for its User. – 'Tron tensed, not knowing from which direction to expect an attack, not sure what he would do wherever it might come from.'

Causality

The interface rose up from the Grid's substructure like a transparent screen, and Flynn planted his palm firmly in the middle of the smooth surface. Energy coalesced with the data he uploaded and filtered through to the other side, where a mirror image rezzed into being. The program was from head to toe a perfect copy.

It was pretty amazing to stare at your own reflection, one that did not breathe but met your gaze, self-aware and _alive_. Flynn felt giddy, like a kid alone in a candy store. This was his tool to make his dream of the Grid come true. He smiled encouragingly and rose from his kneeling position, and after a moment's hesitation, his doppelganger followed suit.

Flynn grinned and returned the expectant stare. "Your name is CLU."

"I am CLU," the program confirmed.

Hearing his own voice out of the mouth of someone else would take some getting used to. But there was a slight difference: the lack of inflection. Then again, Flynn could almost see how the gears started to turn as CLU waited to be given a function. It would be interesting to watch him grow, since this unique program was meant to better itself independently.

This was the first step towards the digital frontier he dreamed of: a true A.I.

"You will create the perfect system."

"I will create the perfect system."

Kevin chuckled; that had sounded like a solemn vow.

"Excellent, man! We'll do it together." He clapped CLU on the shoulder. "Come on then, we've got plenty of work waiting for us."

XXX

The transition from an empty construct to a self-aware program was normally a gradual one, but for CLU, it took only the few steps to get back on the Grid's structure. It was then that he returned his User's smile, feeling content in the knowledge of his purpose.

He followed Kevin into the light, where a whole new world awaited him.

XXX

"Flynn! I lost your location status and was - "

Tron stopped his approach and froze, alarm rushing through his system like tainted energy. His eyes narrowed as he took the sight of the User who was working on a new construct, a transparent shape of half finished walls, surrounded by screens full of code. Something felt off about the scene and Tron trusted his honed instincts enough to initiate a scan. His security checkup was denied, something Kevin would never have done, although he complained to Tron often enough about his constant need to 'baby-sit' him.

The impostor turned around. "Greetings, program," he – _it_ - said with Kevin's voice as it cancelled the pulled-up interfaces with a casual gesture.

Tron felt no need to answer a system anomaly. It only watched him with curiosity as he reached for his Light Disc but Tron noted with grim satisfaction how it flinched back as the blue edge hummed suddenly at its throat.

"Program, identify yourself or - "

"Whoa, what the hell's going on here?" Flynn demanded, stepping out of the half-finished building. Seeing his creation one inch short of being derezzed, he rushed over and tried to restrain the security program. "Chill, man! CLU's a friend!"

Tron ascertained with a quick scan that the User was unharmed before he allowed himself to be pulled back from his target. He lowered his weapon but didn't stop the flow of energy that kept it activated. It would never do to let his guard down.

"Flynn, what is the meaning of this?" Tron asked, but Flynn had turned his back on him and was checking his clone for damage.

"CLU, you alright, man?"

The new program pulled its leather jacket, that had suffered from Tron's firm grip, straight and met his blue-gray stare with Flynn's trademark grin. "I'm fine, Kevin. Good to know that our system is in good hands as far as security is concerned."

"_Our_ system?" Tron echoed, allowing his stance to relax a bit.

Kevin gestured between them. "Yeah man. Tron, meet CLU, the new system MCP. Remember how I told you that I can't be in here all the time? Looks like I solved that little problem. He will run the show in my absence."

Tron processed this new information and its implications for a millicycle. As it came, he was ready to accept the system query and lowered his firewalls to allow the scan. CLU's energy pattern rushed through him and Tron followed the invitation to do the same. He committed the new data to a priority file.

"Finished with introductions?" Kevin asked.

"Yes." Tron returned his Light Disc to the port on his back. "My apologies, CLU, and welcome to the Grid. I'm looking forward to working with you."

He shook the hand the MCP offered him, only slightly thrown by the User-like gesture, realizing that he should probably expect it from a program such as CLU.

"Likewise."

"Man, are you two cold fishes!" Kevin mumbled, exasperated.

XXX

Tron stood to the side, content with securing the parameter and watching Flynn and CLU working on their latest project. Their relentless typing sounded hollow in what would soon cease to be Outland. A data-highway rezzed slowly into being, a growing curve of merging pixels that would soon connect the new sector with the rest of TRON city.

The synchronization between User and program never ceased to amaze Tron, even after all the cycles since CLU's creation. Between their efforts, the Grid was growing more and more complex, a free system with new capabilities. It felt more like home to him than the ENCOM server ever had.

CLU had a large part in that, though – he was a close friend, far more approachable than Flynn, who was always be set apart by the fact that he was a User. Unlike his programmer, CLU never settled for anything less than perfection and he demanded the same high standard from every program he worked with. Tron did not mind at all. It was a known fact one could easily calculate with, a set parameter in the equation. It was quite the opposite of Flynn's disruptive spontaneity that threw the system into chaos more often than not. Needless to say that CLU did not approve of such 'antics'.

The User often quipped that CLU had only inherited his good parts during his compilation and, when especially vexed with his behavior, Tron found himself silently agreeing. Both working in tandem, however, was a sight to behold: perfect balance. Two halves forming a whole, one that should not allow for another to be included. Feeling that way, Tron would have been content to stand aside and simply guard them, fulfilling his function, but -

"Tron! Stop your brooding and get over here!"

XXX

Tron, holding a vial of pure energy in his hand that glowed light blue, stood in the shadowy doorway to the control room and watched his friend work.

CLU stood with his back to him at the terminal. His typing had not ceased for five full millicycles. On the screens around him were whole Grid sections marked with red flags and blinking system warnings. Their alarms had been turned down, but the beeping resounded in the dark room.

CLU's circuitry had dimmed to a worrisome white, the strain too great for comfort. As Tron observed from over his shoulder, the MCP cursed and went some sequences back, to erase faulty lines of coding he had before overlooked.

Distaste curled through Tron's processing and he tensed, feeling the short burst of anger directed at the User. This cascade failure was a threat, one that was the result of the User's experiments, but Flynn had left dealing with the fallout to CLU, and chosen to move on to the next project instead of helping to fix this.

The emotion was fleeting, though. The User had, no doubt, other urgent matters to attend to, and CLU needed Tron to be focused. There was no logic in worrying over things he could not change.

He moved over to CLU's side and offered him the vial. The sound of rapid typing ceased for the moment it took the MCP to grasp, drain and derezz it. Tron's concern eased slightly as the energy replenished CLU's reserves in a rush of bright yellow.

"Your orders?"

"Evacuation of Sector 3," CLU said into a moment of silence. He finally turned around to look at Tron, but as angry as he had sounded, his face was just pale in defeat.

Shock rushed through Tron. "Is there no other way?"

"No!" CLU snapped, and Tron could see the effort it took him to maintain his composure.

"I'm sorry," they both said, and neither was sure what they really apologized for.

CLU managed a strained smile. "I'm out of options, man," he said, rubbing at the bridge of his nose, just like Flynn when the User was frustrated. His hands curled into fists at his sides as another alarm sounded. "Without Flynn's master key, all I can do is minimize the damage."

Tron nodded gravely. "I'm on my way."

Leaving, he realized that CLU had stopped calling his User 'Kevin' cycles ago.

XXX

They stood side by side and watched as it happened: buildings flared up and turned transparent, letting their codes shine through like green threads before a dark sky. Fissures spread in ugly lines through the structures as they lost integrity and fell apart. The towers shattered into pieces as if caught in an explosion. Their bright data-bits rained to the ground in cascades, catching the light of the lightnings overhead and making a tinkling sound like bells on impact.

The last batch of evacuated programs stood behind Tron and CLU, staring. They clung to each other in desperation. Their homes and the work of thousands of cycles were ground to dust in mere klicks.

"Here they come," CLU warned, appearing calm to all but Tron, who felt his energy fluctuate wildly in mourning.

His friend had shrugged his hand off once and would not find any comfort in the gesture anyway, so he did not try again. Tron could not pinpoint his own emotions over the matter; ever since Kevin had become distant he felt... disconnected.

Tron spotted them, too: swarms of gridbugs, a carpet of red lights, rising from the Outlands to feed on the data-bits - and anything else unfortunate enough to cross their path. Screeching filled the air, a threat, a warning.

"CLU, please escort them to the shelter. I'll take care of the bugs until reinforcements arrive."

CLU nodded and turned away, herding the lesser programs to the waiting transport.

XXX

CLU spun around. His roundhouse kick derezzed one bug on contact and sent two more flying to shatter on impact. He had to jump to catch his Light Disc - it had veered off course.

He had never before fought like this, with vicious abandon, not calculating; consequences be damned. It worried him, in some removed corner of his processor, but he needed to purge the anger from his system or he feared he might do something unforgivable.

Sharp pain rushed up his arm: one gridbug had attached itself to his wrist and tried to dissolve the lightsuit to reach his core data, sending him reeling as his firewalls came online. Sensing a weakness, the rest of the swarm closed in.

Their attack came to a halt as a blue blur sliced through them, derezzing the bug that clung to CLU. He could see Tron out of the corner of his eye, catching his Light Disc and moving in to cover him.

Even after the deed was done, Tron said nothing. Having seen him fight, CLU knew he understood all too well.

XXX

"He will abandon us."

"CLU - "

"He already did."

Tron remained silent. He was hurting too, deprived of his main purpose to assist the User as Kevin Flynn's presence faded more from the Grid with every passing cycle. In the face of CLU's anger, it became increasingly difficult to defend the Creators actions - but he could not stop trying. CLU needed Flynn on an even more visceral level than Tron did - there was no term of relation that did not apply to them. But his friend had ceased to be receptive to words and so, instead of saying anything, he pulled CLU into a hug.

CLU was rigid in his arms but then his familiar energy signature spiked and settled, realizing the depth of Tron's own desperation; reading it.

"I'm sorry," CLU murmured, and tugged him closer.

That was the moment in which Tron realized he had needed the contact, too.

XXX

CLU's circuitry flashed violet. "This is our world. It's the only one we programs have and you, our _Creator_, allow it to fall apart!"

"Enough!"

Tron stepped forward quickly. He used his own body to shield Flynn and grabbed CLU's hand, yanking it away from his Light Disc. The MCP resisted and instinct took over – _protect the User!_ - and a moment later, CLU looked up to him from the ground. He could only stare back in his bright blue eyes; it took him a moment to see the gash from which data-bits trickled down.

"CLU, please stop this."

The MCP stood up, stemming the data-loss with one hand. "Will you side with him?" CLU asked in a quiet voice that sent chills down Tron's spine. "Will you derezz me if I don't stand down? You are always fighting for the Users, after all – and this one looks ready to give you the order."

Tron could feel Kevin tense behind him and knew he was angry enough to be tempted. Only a dozen cycles before he would have laughed at the thought that Flynn might order him to harm CLU - now the possibility loomed over him and filled him with dread.

"Maybe I should," Kevin spat, pale and shaking with anger.

"I trusted you! You said we were going to create the perfect system. Together! Why, Flynn? Why? We need you – _I_ need you!"

Tron tensed, not knowing from which direction to expect an attack, not sure what he would do wherever it might come from.

"Enough, CLU! I wrote you, I won't be questioned by a program!" Kevin shouted and turned away towards the Solar Sailer.

"We're not your tools!"

XXX

The User was gone. The bright blue star had vanished in the east, sealing the portal shut behind Kevin Flynn, the Creator.

XXX

CLU was forced to stop his Light Cycle a good distance away from his destination because the ground had become too unstable to support more than a single program's weight. Fissures and holes gaped everywhere, glowing green from the roiling code below.

He didn't bother to pick up his baton – the odds he had calculated spoke against his return. CLU jumped over a crack and broke into a run, intent on reaching the core as fast as possible.

He could only hope that his diversion would buy him enough time to finish this before Tron grew suspicious. The fact that Tron had avoided him after their argument should work in his favor.

It was typical Tron behavior to blame not Flynn but himself and being ashamed to doubt the User as much as CLU did, something the security program did not say out loud but that was a fact ingrained in the weary way he held himself. Not that CLU had expected differently; Tron was too defined by his directive to act otherwise. Maybe some cycle his friend would be able to evolve beyond that.

CLU could not stand by and watch another sector disintegrate. It was his duty as the system administrator to protect his fellow programs and maintain the Grid, he just did it on a different scale than Tron. Flynn had created him as a copy of himself to do just that and now it was time to test how successful the User truly had been. If he failed here, it would only marginally speed up a destructive process that then would be proven as unstoppable without the User's help.

CLU stopped and kneeled down to touch the ground. The contact together with his focused intent derezzed the layers down to the energy supply network. Its source was unknown to him - Flynn had only ever told him that it lay in the outside world.

He jumped down and felt the charged up atmosphere crackle along his lightsuit in the dark tunnel. Blue energy beams formed a crisscrossing net, humming a low, constant tune. Up ahead, CLU was greeted by eerie silence. The last connection between the two sectors had fully disintegrated, leaving the energy to overload the border section.

CLU did not hesitate and walked into the pool of dazzling light to act as a conduit. The energy slammed into him with brute force, burning his code and files away, data-bits scattered around him as he lost integrity.

CLU screamed but did not relent. He pushed forward and used his arms and hands to guide the beam. The connection jolted through him, drowning him in system alerts and something exploded, hurling him away.

Everything went dark long before he hit the ground.

XXX

The energy wave came out of nowhere, a bright light that left Tron no chance to react. Its pulse swept him and his Light Cycle from the highway, engulfing him in a torrent of white that tugged him into emergency stasis.

He was slow to reboot. Sounds, tactile sensations, his sight and all input suffered from a delay, giving his surroundings a hazy quality, but that could not stop Tron from scrambling to his feet as he saw a yellow glow not far away.

It was CLU, lying on the slowly rerezzing ground. An image of Flynn, using his body as a conduit for the Solar Sailor's transport beam, rose unbidden to the forefront of Tron's processor. It filled him with dread at what he would find.

"CLU!" Tron almost choked on the name, seeing the damage. He dropped to his knees beside the dark body. Data-bits chipped away to form a heap around the still MCP. Only the slightest flicker of an impulse rushed through the white circuitry.

Tron felt lost. He didn't know what to do; he was no User, could not even access CLU's identity disc to manipulate the code it contained to freeze all processes, and he didn't carry any energy with him. He was reluctant to even risk touching CLU, afraid that the unstable program might shatter under his hand, but Tron had no choice. His connection to the system was still down and no help would come for them. Most other programs would not even have rebooted after the shock wave, because their firewalls were far less advanced.

Tron hissed as discharge ran up his arms, meeting his descending hands, but he managed to pick CLU up. He was stiff and cold in his arms and a void to all his scans, but he didn't disintegrate.

Yet.

XXX

The golden light traveled slowly over CLU's dark body, scanning him so that the gathered repair programs could assess the whole damage. Klicks went by while they went over the results, and Tron knew what they would tell him even before they had finished: that the damage was too extensive, that there was no hope for recovery.

Tron could not stop hoping though - CLU was Kevin's greatest creation, unique among the Grid's programs; he should be able to survive. Tron would not lose the only friend he had left.

'_Life's not fair, Tron_,' the memory of Kevin Flynn whispered in his mind.

XXX

Seeing CLU like this, lying immobile on a metal slab that shined through his damaged body, felt wrong in a way only comparable to the separation from Flynn. Tron had only ever known him as a vibrant presence that commanded the attention of every program in the same room.

Tron could only stand by and wait, though, and he hated every klick of it. But as the cycles changed, he saw the deletion process slow against all odds and CLU's body solidifying. Somehow, miraculously, CLU's system was capable of self-repair – like a User's.

He had not moved from his guarding position besides CLU's berth once when the MCP finally rebooted. The first sign of consciousness was a weak rush of energy that slowly crept through the dark circuitry until all patterns were lit a pale yellow.

CLU did not open his eyes but his head rolled slightly into Tron's direction. "The sector -" His voice was faint and full of static.

Tron reached out and placed his hand on CLU's chest, opening a connection to transfer some of his own energy to him. It stung as the flow was reversed in rejection but he felt more relieved than offended. CLU would not have been too proud to accept his help had he truly needed it.

"- is safe," Tron said, but his intended reassurance was replaced by a sharp: "Don't you dare do that again!"

CLU managed a smile, but it faded quickly. "Flynn?"

Tron's silence was answer enough, and CLU's face fell in a way that spoke of his weakness; he looked lost.

Seeing it changed something in Tron he could not yet name, but the feeling _burned_.

XXX

The blue star shone brightly, announcing the presence of a User for the first time in over a one hundred cycles. Tron derezzed the last remnants of a gridbug swarm and grabbed his baton. He knew what he had to do.

XXX

It took Kevin Flynn's dumbfounded stare for Tron to realize that his circuits glowed now a bright yellow, but he was not surprised.

He could not allow the User to leave again; CLU needed his master key to save the Grid. Flynn had lost any right to it.

Tron reached for his Light Disc.

End

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